A Li2O—Al2O3—SiO2 based crystallized glass in which a Li2O—Al2O3—SiO2 based crystal such as a β-quartz solid solution (Li2O.Al2O3.nSiO2 [4>n≧2]) or a β-spodumene solid solution (Li2O.Al2O3.nSiO2 [n≧4]) is precipitated has a low coefficient of thermal expansion and high mechanical strength and hence has excellent thermal characteristics. In addition, it is possible to regulate the kind of a precipitated crystal by appropriately adjusting heat treatment conditions in a crystallization step, so that a transparent crystallized glass (a β-quartz solid solution precipitates as a main crystal) and an opaque crystallized glass (a β-spodumene solid solution precipitates as a main crystal) can be easily produced. Making use of such characteristics, the Li2O—Al2O3—SiO2 based crystallized glass has been widely used as materials such as front windows of oil stoves, wood stoves, and the like, substrates for high-technology products such as color filter substrates and image sensor substrates, setters for firing electronic components, trays for microwave ovens, top plates of electromagnetic cookers, and window glasses for fire-retarding doors.
Moreover, there has been known a Li2O—Al2O3—SiO2 based crystallized glass in which a coloration component such as V2O5 is added to a Li2O—Al2O3—SiO2 based crystallized glass to color it dark-brown. The colored crystallized glass hardly transmits a visible light but has a high infrared transmittance, so that the glass has been used as top plates of cookers utilizing infrared rays.
Incidentally, in the case of producing a Li2O—Al2O3—SiO2 based crystallized glass, it is necessary to perform melting at a high temperature exceeding 1,400° C. Therefore, as a fining agent to be added to a glass batch, As2O3 or Sb2O3 capable of generating a lot of a fining gas at the time of melting at the high temperature has been used. However, since As2O3 and Sb2O3 exhibit strong toxicity, attention should be paid so as not to contaminate the environment at the production process of the glass, at the time of treating a waste glass, or at a similar time.
Accordingly, SnO2 has been proposed as a substitute fining agent for As2O3 or Sb2O3 (e.g., see Patent Reference 1).